On the website of Smythson's, purveyor of luxury goods and personalised stationery, there is a slim and elegant Panama notebook for sale at £40. It is bound in bright blue leather, almost precisely the same colour the Conservatives used for election campaign posters, and the front cover is embossed with the words: "Now panic and freak out."

Samantha Cameron, creative director of Smythson's in Bond Street, London, for 14 years until last week, could be forgiven for thinking the same. As the wife of the youngest prime minister in almost 200 years, she has been thrust into the harsh and unforgiving glare of the limelight. Last Tuesday night, when David Cameron stood on the steps of 10 Downing Street as leader of a new coalition government, his pregnant wife smiled sweetly for the press and put on a media-friendly show of doting support. The following morning, she had cameras unceremoniously shoved in her face as she took the couple's children – Nancy, six, and Arthur, four – to school.

"Her whole life is now in danger of being taken over by media people," says Max Clifford, the celebrity publicist. "My advice to her would be: don't fall into that trap. Start as you mean to go on and be yourself. She's not the prime minister, she's the prime minister's wife and she has never sought to be elected."

Yet Samantha Cameron is finding that even the most mundane aspects of her daily life are apparently of great interest to the world at large. Her relationship with her husband has become public property and she is trailed by protection officers. "She will face inevitable strains," says Sandra Howard, wife of the former Conservative leader Michael Howard and author of several novels including A Matter of Loyalty. "I loved the detectives who were with us, but there's something about pulling out weeds in your garden when you know someone's looking at you on a camera several feet away that is very restrictive."

Perhaps those restrictions are already beginning to chafe. Although she is, by all accounts, a gifted and incisive businesswoman, Samantha, 39, has stepped down from her role at Smythson's and chosen to work two days a week as "creative consultant". She must have been keenly aware of the barrage of criticism faced by Cherie Blair, who battled on as a full-time barrister while her husband was prime minister, only to be pilloried for "cashing in" on the privileges of office.

"I think it's an extremely sensible decision," says Alicia Collinson, the barrister wife of immigration minister Damian Green and author of Politics for Partners: How to Live with a Politician. "Otherwise everyone would be talking about leather goods and handbags rather than concentrating on her husband's politics."

Still, Samantha's decision to walk away from a job she enjoyed must have been difficult, especially for a woman who has never courted public attention. Indeed when the Camerons moved into their home in Notting Hill, west London, in 2006, a neighbour idly speculated that the next time removal trucks pulled up the family would no doubt be moving to No 10. Samantha is reported to have replied: "I fucking hope not." She has always been slightly edgier than her husband – she sports a dolphin tattoo on her right ankle and hung out in the same pub as trip-hop musician Tricky when she was an art student in Bristol – and is seen by Tory strategists as an asset in giving "Dave" some street credibility.

Phil Hall, a former editor of the News of the World who now runs a PR consultancy, says that the "overwhelming task" of being a modern prime minister's wife makes it almost impossible to carry on working full-time. "She'll be travelling the world with young children and living at No 10 will bring with it the inevitable functions and dinners," he says. "And she's about to have a baby – it's full on, especially because David Cameron is not in a position to be the stay-at-home dad and cover for her.

"My advice would be absolutely to be herself. People are so suspicious of Downing Street spin and presentation. They want substance over style…

"I'd advise her to do nothing – no interviews – because I don't think it has any relevance to David Cameron's job. He's going to be judged on how he turns round the economy, not on what his wife says. Trying to use her as a political pawn will arouse the suspicions of the public."

The complexities of Samantha Cameron's new life underline how demanding the job of prime ministerial spouse has become. Once the role was relatively straightforward: wives were expected to smile lots and say little. Their function was to be a consort in public and a mother and housewife in private.

But with the rising popularity of high-profile political partners such as Michelle Obama in the US and Carla Bruni-Sarkozy in France, the role of prime ministerial wife seems to have expanded into that of an unofficial first lady. "It really is a new thing," says Sandra Howard. "There's a tendency to want to show the whole package, to show the human side of a politician."

Now the wife in No 10 must not only be a tireless charity campaigner and grow vegetables in the back garden as part of an anti-obesity drive, but also has the pressure of looking impeccably groomed at all times.

"Michelle Obama has had a massive impact in fashion terms," says Rebekah Roy, a fashion stylist and blogger whose clients include Sophie Ellis Bextor, Kaiser Chiefs and Billy Idol. "She really brought fashion to the fore and showed that you could dress beautifully and still be an incredibly intelligent woman. The key to her look is that her clothes don't have to be expensive, and that's what I'd suggest for Samantha Cameron – she could wear a dress from an up-and-coming British designer for an event and then throw on an M&S coat so that people can still relate to her. Whatever she wears, she will have to look good. She's the prime minister's wife and we want somebody to represent British fashion, which is one of our biggest exports. We don't want someone to look just normal."

Alicia Collinson thinks Mrs Cameron, who once harboured ambitions to be a professional painter, will probably emulate Norma Major, who eschewed media attention in favour of pursuing pet projects such as writing a biography of opera singer Joan Sutherland. "I suspect they are probably quite similar characters," says Collinson, who first met Samantha in 1994 when David, then her boyfriend, was competing against Collinson's husband to be selected as parliamentary candidate for Ashford, Kent. "Normally, you would probably feel a degree of competitiveness towards the other spouses, especially towards this young, glamorous girlfriend," says Collinson. "In fact, I ended up giving her some safety pins because she'd come wearing this very fashionable wrap-around skirt and we had to sit on a platform while our spouses made their speeches and she realised she was going to be showing too much leg.

"I'd never met her before, but the vulnerability she exuded meant I didn't think, 'Oh good, she's going to make a show of herself' but wanted to help. She evoked that reaction in me, even then. And she was very grateful for the safety pins." Whatever happens during the next few months of her husband's first term in office, Samantha Cameron will need more than just safety pins to avoid putting herself on display.